The present invention relates to a heat exchanger for transferring heat from one fluid to another fluid, comprising a plurality of metallic tube continuously formed into four discrete helically wound coils, each coil having at least four turns, the coils being spatially placed such that axis of all the four helical coils of each bank are substantially in one common plane, the axis of each helical coil is at an angle of 90.degree. to the adjacent helical coil, wherein number of banks is from 2 to 10 and ratio of diameter of the helical coil to the diameter of the tube is at least 10:1.